On the mechanism of the antitumor activity of ferrocenium derivatives

Ferrocenyl Azoles: Versatile N-Containing Heterocycles and their Anticancer Activities

The medicinal chemistry of ferrocene has gained its momentum after the discovery of biological activities of ferrocifen and ferroquine. These ferrocenyl drugs have been designed by replacing the aromatic moiety of the organic drugs, tamoxifen and chloroquine respectively, with a ferrocenyl unit. The promising biological activities of these ferrocenyl drugs have paved a path to explore the medicinal applications of several ferrocenyl conjugates. In these conjugates, the ferrocenyl moiety has played a vital role in enhancing or imparting the anticancer activity to the molecule. The ferrocenyl conjugates induce the cytotoxicity by generating reactive oxygen species and thereby damaging the DNA. In medicinal chemistry, the five membered nitrogen heterocycles (azoles) play a significant role due to their rigid ring structure and hydrogen bonding ability with the biomolecules. Several potent drug candidates with azole groups have been in use as chemotherapeutics. Considering the importance of ferrocenyl moiety and azole groups, several ferrocenyl azole conjugates have been synthesized and screened for their biological activities. Hence, in the view of a wide scope in the development of potent drugs based on ferrocenyl azole conjugates, herein we present the details of synthesis and the anticancer activities of ferrocenyl compounds bearing azole groups such as imidazole, triazoles, thiazole and isoxazoles.

Oxidation-derived anticancer potential of sumanene-ferrocene conjugates

An effective synthetic protocol towards the oxidation of sumanene-ferrocene conjugates bearing one to four ferrocene moieties has been established. The oxidation protocol was based on the transformation of FeII from ferrocene to FeIII-containing ferrocenium cations by means of the treatment of the title organometallic buckybowls with a mild oxidant. Successful isolation of these ferrocenium-tethered sumanene derivatives 5-7 gave rise to the biological evaluation of the first, buckybowl-based anticancer agents, as elucidated by in vitro assays with human breast adenocarcinoma cells (MDA-MB-231) and embryotoxicity trials in zebrafish embryos supported with in silico toxicology studies. The designed ferrocenium-tethered sumanene derivatives featured attractive properties in terms of their use in cancer treatments in humans. The tetra-ferrocenium sumanene derivative 7 featured especially beneficial biological features, elucidated by low (<40% for 10 μM) viabilities of MDA-MB-231 cancer cells together with a 1.4-1.7-fold higher viability of normal cells (human mammary fibroblasts, HMF) for respective concentrations. Compound 7 featured significant cytotoxicity against cancer cells thanks to the presence of sumanene and ferrocenium moieties; the latter motif also provided the selectivity of anticancer action. The biological properties of 7 were also improved in comparison with those of native building blocks, which suggested the effects of the presence of the sumanene skeleton towards the anticancer action of this molecule. Ferrocenium-tethered sumanene derivatives exhibited potential towards the generation of reactive oxygen species (ROS), responsible for biological damage to the cancer cells, with the most efficient generation of the tetra-ferrocenium sumanene derivative 7. Derivative 7 also did not show any embryotoxicity in zebrafish embryos at the tested concentrations, which supports its potential as an effective and cancer-specific anticancer agent. In silico computational analysis also showed no chromosomal aberrations and no mutation with AMES tests for the compound 7 tested with and without microsomal rat liver fractions, which supports its further use as a potent drug candidate in detailed anticancer studies.

Effects of Ferrocene and Ferrocenium on MCF-7 Breast Cancer Cells and Interconnection with Regulated Cell Death Pathways

The effects of ferrocene (Fc) and ferrocenium (Fc+) induced in triple negative human breast cancer MCF-7 cells were explored by immunofluorescence, flow cytometry, and transmission electron microscopy analysis. The different abilities of Fc and Fc+ to produce reactive oxygen species and induce oxidative stress were clearly observed by activating apoptosis and morphological changes after treatment, but also after tests performed on the model organism D. discoideum, particularly in the case of Fc+. The induction of ferroptosis, an iron-dependent form of regulated cell death driven by an overload of lipid peroxides in cellular membranes, occurred after 2 h of treatment with Fc+ but not Fc. However, the more stable Fc showed its effects by activating necroptosis after a longer-lasting treatment. The differences observed in terms of cell death mechanisms and timing may be due to rapid interconversion between the two oxidative forms of internalized iron species (from Fe2+ to Fe3+ and vice versa). Potential limitations include the fact that iron metabolism and mitophagy have not been investigated. However, the ability of both Fc and Fc+ to trigger different and interregulated types of cell death makes them suitable to potentially overcome the shortcomings of traditional apoptosis-mediated anticancer therapies.

Ferrocene-Based Drugs, Delivery Nanomaterials and Fenton Mechanism: State of the Art, Recent Developments and Prospects

Ferrocene has been the most used organometallic moiety introduced in organic and bioinorganic drugs to cure cancers and various other diseases. Following several pioneering studies, two real breakthroughs occurred in 1996 and 1997. In 1996, Jaouen et al. reported ferrocifens, ferrocene analogs of tamoxifen, the chemotherapeutic for hormone-dependent breast cancer. Several ferrocifens are now in preclinical evaluation. Independently, in 1997, ferroquine, an analog of the antimalarial drug chloroquine upon the introduction of a ferrocenyl substituent in the carbon chain, was reported by the Biot-Brocard group and found to be active against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Ferroquine, in combination with artefenomel, completed phase IIb clinical evaluation in 2019. More than 1000 studies have been published on ferrocenyl-containing pharmacophores against infectious diseases, including parasitic, bacterial, fungal, and viral infections, but the relationship between structure and biological activity has been scarcely demonstrated, unlike for ferrocifens and ferroquines. In a majority of ferrocene-containing drugs, however, the production of reactive oxygen species (ROS), in particular the OH. radical, produced by Fenton catalysis, plays a key role and is scrutinized in this mini-review, together with the supramolecular approach utilizing drug delivery nanosystems, such as micelles, metal-organic frameworks (MOFs), polymers, and dendrimers.

Ferrocene-triazole conjugates: do we know why they are biologically active?

The bioorganometallic chemistry of ferrocene has been gaining significance in recent years. This review presents ferrocene-triazole conjugates displaying significant biological properties. The conjugates have been synthesized via azide-alkyne cycloaddition reactions. The data are summarized according to the type of activity (anticancer, antibacterial and/or antifungal, antiprotozoal, and other effects). The results of studies concerning the understanding of the role of the ferrocene core in their biological activity are highlighted. While generally the mode of action of these organometallic species remains unclear, the importance of redox properties of ferrocene has been postulated in several cases.

Potent Ruthenium-Ferrocene Bimetallic Antitumor Antiangiogenic Agent That Circumvents Platinum Resistance: From Synthesis and Mechanistic Studies to In Vivo Evaluation in Zebrafish

Emergence of resistance in cancer cells and dose-limiting side effects severely limit the widespread use of platinum (Pt) anticancer drugs. Multi-action hybrid anticancer agents that are constructed by merging two or more pharmacophores offer the prospect of circumventing issues of Pt drugs. Herein, we report the design, synthesis, and in-depth biological evaluation of a ruthenium-ferrocene (Ru-Fc) bimetallic agent [(η6-p-cymene)Ru(1,1,1-trifluoro-4-oxo-4-ferrocenyl-but-2-en-2-olate)Cl] and its five analogues. Along with aquation/anation chemistry, we evaluated the in vitro antitumor potency, Pt cross-resistance profile, and in vivo antiangiogenic properties. A structure activity analysis was performed to understand the impact of Fc, CF3, and p-cymene groups on the anticancer potency of the Ru-Fc hybrid. Finally, in addition to assessing cellular uptake and intracellular distribution, we demonstrated that the Ru-Fc hybrid binds to nucleophilic biomolecules and produces reactive oxygen species, which causes mitochondrial dysfunction and induces ER stress, leading to poly(ADP-ribose) polymerase-mediated necroptotic cell death.

Modeling Absolute Redox Potentials of Ferrocene in the Condensed Phase

Absolute thermodynamic quantities for critical chemical reactions are needed to determine the role of solvents and reactive environments in catalysis and electrocatalysis. Theoretical methods can provide such quantification but are often hindered by the innate complexity of electron correlation and dynamic relaxation of solvent environments. We present and validate a protocol for calculating the redox potentials of the ferrocene/ferrocenium redox pair in acetonitrile. Equation-of-motion and effective fragment potential (EFP) methods are used to characterize the adiabatic and vertical ionization potentials as well as the electron affinity processes. We benchmark molecular mechanics against the EFP model to show the differences in the ferrocene electronic polarizability in two redox states. Our best estimate of the redox potential (4.94 eV) agrees well with the experimental value (4.93 eV). This demonstrates the ability of modern computational methods to predict absolute redox potentials quantitatively and to quantify the correlation of dynamic effects, which underlie their origin.

Impact of Coordination Mode and Ferrocene Functionalization on the Anticancer Activity of N-Heterocyclic Carbene Half-Sandwich Complexes

The substitution of phenyl rings in established drugs with ferrocenyl moieties has been reported to yield compounds with improved biological activity and alternative modes of action, often involving the formation of reactive oxygen species (ROS). Translating this concept to N-heterocyclic carbene (NHC) complexes, we report here organometallics with a piano-stool structure that feature di- or tridentate ligand systems. The ligands impacted the cytotoxic activity of the NHC complexes, but the coordination modes seemed to have a limited influence, which may be related to the propensity of forming the same species in solution. In general, the stability of the complexes in an aqueous environment and their reactivity to selected biomolecules were largely dominated by the nature of the metal center. While the complexes promoted the formation of ROS, the levels did not correlate with their cytotoxic activity. However, the introduction of ferrocenyl moieties had a significant impact on the antiproliferative potency of the complexes and, in particular, some of the ferrocenyl-functionalized compounds yielded IC₅₀ values in the low μM range.

Ferrocene-Bearing Dodecylphthalocyanines: Synthesis, Spectroscopic and Electrochemical Behavior

Ferrocenylbutoxy-bearing dodecylated phthalocyanines, MPc(C₁₂H₂₅)_x(OC₄H₈Fc)_y with M = 2H (compound series 6 and 8) or Zn (compound series 5, 7 and 9), x ≤ 8 and y ≤ 4, were synthesized through either metal-free statistical condensation between 3,6-bis(dodecyl)phthalonitrile, 2, and 4- (1), or 3-(4'-ferrocenylbutoxy)phthalonitrile, 4, or a zinc template statistical condensation between 4,5-bis(dodecyl)phthalonitrile, 3, and 1 in the presence of anhydrous zinc acetate, or by zinc insertion into metal-free phthalocyanines. Compounds were designed to have eight nonperipheral dodecyl substituents, six nonperipheral dodecyl, either one peripheral or one nonperipheral 4'-ferrocenylbutoxy substituent, four nonperipheral dodecyl and two peripheral 4'-ferrocenylbutoxy substituents, or four peripheral 4'-ferrocenylbutoxy substituents. The compound having six peripheral dodecyl and one peripheral 4'-ferrocenylbutoxy substituents was also synthesized. Metal-free and zinc complex Q-band maximum absorption wavelengths increased nonlinearly from 704 to 725 nm for the Q_y-band of metal-free compounds, or from 676 to 699 nm for the Q-band of zinc complexes in moving from all peripheral-substituted to all non-peripheral-substituted complexes. A rare case of accidental Q-band degeneracy where only one electronic Q-band is observed for asymmetrical zinc complexes NOT having D_4h symmetry, compounds 5, 7b-e, and 9b, is also described. X-ray photoelectron spectroscopy (XPS) differentiated between four types of phthalocyanine nitrogen atoms; binding energies were ca. 399.8 (N-H), 398.1 (N_meso), 397.8 (N_core), and 398.7 eV (N-Zn), respectively. An electrochemical study of these compounds revealed up to five different redox processes in dichloromethane but only three in tetrahydrofuran (THF). The first ring-based oxidation of both metal-free compounds 6a-e and zinc phthalocyanines 7a-e exhibited a near-linear increase in peak anodic potentials, E_pa, with the systematic replacement of two nonperipheral dodecyl substituents with one peripheral 4'-ferrocenylbutoxy group. When four 4'-ferrocenylbutoxy groups were substituted on the phthalocyanine macrocycle, aggregation of the first oxidized species was observed. Zinc insertion into metal-free phthalocyanines lowered formal redox potentials. An electrochemical scheme consistent with electrochemical results is provided.

Synthetic and DFT Modeling Studies on Suzuki–Miyaura Reactions of 4,5-Dibromo-2-methylpyridazin-3(2H)-one with Ferrocene Boronates, Accompanied by Hydrodebromination and a Novel Bridge-Forming Annulation In Vitro Cytotoxic Activity of the Ferrocenyl–Pyridazinone Products

This paper presented the efficiency of different Pd-based catalytic systems in a series of SM reactions of 4,5-dibromo-2-methylpyridazin-3(2H)-one with ferroceneboronic acid, ferrocene-1,1′-diboronoc acid, and its bis-pinacol ester. In addition to the disubstituted product, these transformations afford substantial amounts of isomeric 4- and 5-ferrocenyl-2-methylpyridazin-3(2H)-ones, and a unique asymmetric bi-pyridazinone-bridged ferrocenophane with a screwed molecular architecture. The reactions of phenylboronic acid, conducted under the conditions, are proven to be the most reductive in the conversions of ferroceneboronic acid, and produce 2-methyl-4,5-diphenylpyridazin-3(2H)-one as single product, supporting our view about solvent-mediated hydrodehalogenations that are supposed to proceed via the assistance of the ferrocenyl group present in the reaction mixture, or attached to the bromo-pyridazinone scaffold, which is constructed in the first SM coupling of the heterocyclic precursor. A comparative DFT modelling study on the structures and possible transformations of relevant bromo-, ferrocene- and phenyl-containing carbopalladated intermediate pairs was carried out, providing reasonable mechanisms suitable to account for the apparently surprising regioselectivity of the alternative hydrodebromination processes, and for the formation of the ferrocenophane product. Supporting the results of DFT modelling studies, the implication of DMF as a hydrogen transfer agent in the hydrodebromination reactions is evidenced by deuterium labelling experiments using the solvent mixtures DMF-d7–H2O (4:1) and DMF–D2O (4:1). The organometallic products display antiproliferative effects on human malignant cell lines.

New ferrocene-integrated multifunctional guanidine surfactants: synthesis, spectroscopic elucidation, DNA interaction studies, and DFT calculations

Investigation of three new ferrocene appended guanidines as potential surfactants, antioxidants and DNA binders with DFT measurements.

A Ru(ii)-arene-ferrocene complex with promising antibacterial activity

The evolution of high virulence bacterial strains has necessitated the development of novel therapeutic agents to treat resistant infections.

Heterogeneity of Response to Iron-Based Metallodrugs in Glioblastoma Is Associated with Differences in Chemical Structures and Driven by FAS Expression Dynamics and Transcriptomic Subtypes

Glioblastoma (GBM) is the most frequent and deadliest primary brain cancer in adults, justifying the search for new treatments. Some members of the iron-based ferrocifen family have demonstrated a high cytotoxic effect on various cancer cell lines via innovative mechanisms of action. Here, we evaluated the antiproliferative activity by wst-1 assay of six ferrocifens in 15 molecularly diverse GBM patient-derived cell lines (PDCLs). In five out of six compounds, the half maximal inhibitory concentration (IC₅₀) values varied significantly (10 nM < IC₅₀ < 29.8 µM) while the remaining one (the tamoxifen-like complex) was highly cytotoxic against all PDCLs (mean IC₅₀ = 1.28 µM). The pattern of response was comparable for the four ferrocifens bearing at least one phenol group and differed widely from those of the tamoxifen-like complex and the complex with no phenol group. An RNA sequencing differential analysis showed that response to the diphenol ferrocifen relied on the activation of the Death Receptor signaling pathway and the modulation of FAS expression. Response to this complex was greater in PDCLs from the Mesenchymal or Proneural transcriptomic subtypes compared to the ones from the Classical subtype. These results provide new information on the mechanisms of action of ferrocifens and highlight a broader diversity of behavior than previously suspected among members of this family. They also support the case for a molecular-based personalized approach to future use of ferrocifens in the treatment of GBM.

Redox-dependent cytotoxicity of ferrocene derivatives and ROS-activated prodrugs based on ferrocenyliminoboronates

Four ferrocene derivatives - ferrocenecarboxylic acid, ferrocenium salt, ferroceneboronic acid, and aminoferrocene - were characterized electrochemically, and their cytotoxicity was probed using cancer cells (line MG-63). We related the observed cytotoxicity with the determined redox potentials of these four ferrocenes - aminoferrocene with its lowest redox potential exhibited the highest cytotoxicity. Thus, we synthesized four derivatives consisting of aminoferrocene and phenylboronic acid residue with the intent to employ them as ROS-activated prodrugs (ROS - reactive oxygen species). We characterized them and studied their time-dependent stability in aqueous environments. Then, we performed electrochemical measurements at oxidative conditions to confirm ROS-responsivity of the synthesized molecules. Finally, the cytotoxicity of the synthesized molecules was tested using cancer MG-63 cells and noncancerous NIH-3T3 cells. The experiments revealed sought behaviour, especially for para-regioisomers of synthesized ferrocenyliminoboronates.

Preparation and the anticancer mechanism of configuration-controlled Fe(II)-Ir(III) heteronuclear metal complexes

A series of configuration-controlled Fe(ii)-Ir(iii) heteronuclear metal complexes, including ferrocene and half-sandwich like iridium(iii) complex units, have been designed and prepared. These complexes show better anticancer activity than cisplatin under the same conditions, especially cis-configurational ones. Laser confocal microscopy analysis confirms that the complexes follow a non-energy-dependent cellular uptake mechanism, accumulate in lysosomes (pearson co-localization coefficient: ∼0.7), lead to lysosomal damage, and eventually induce apoptosis. These complexes can reduce the mitochondrial membrane potential, disturb the cell circle, catalyze the oxidation of nicotinamide-adenine dinucleotide (NADH) and increase the levels of intracellular reactive oxygen species (ROS), following an anticancer mechanism of oxidation. In addition, the complexes could bind to serum protein, and transport through it. Above all, the Fe(ii)-Ir(iii) heteronuclear metal complexes hold promise as potential anticancer agents for further study.

Photodynamic activity and photoantimicrobial chemotherapy studies of ferrocene-substituted 2-thiobarbituric acid

A ferrocene-substituted thiobarbituric acid (FT) has been synthesized to explore its photophysical properties and photodynamic and photoantimicrobial chemotherapy activities. FT has an intense metal-to-ligand charge transfer (MLCT) band at ca. 575 nm. The ferrocene moiety of FT undergoes photooxidation to form a ferrocenium species which in turn produces hydroxyl radical in an aqueous environment, which was confirmed via the bleaching reaction of p-nitrosodimethylaniline (RNO). FT exhibits efficient PDT activity against MCF-7 cancer cells with an IC₅₀ value of 5.6 μM upon irradiation with 595 nm for 30 min with a Thorlabs M595L3 LED (240 mW cm^-2). Photodynamic inactivation of Staphylococcus aureus and Escherichia coli by FT shows significant activity with log reduction values of 6.62 and 6.16 respectively, under illumination for 60 min at 595 nm. These results demonstrate that ferrocene-substituted thiobarbituric acids merit further study for developing novel bioorganometallic PDT agents.

Synthesis, electrochemistry, DNA binding and in vitro cytotoxic activity of tripodal ferrocenyl bis-naphthalimide derivatives

A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized and characterized. All of the bis-naphthalimide derivatives exhibited good DNA binding ability which was confirmed by ethidium bromide (EB) displacement experiment and ultraviolet (UV)-visible absorption titration. And the binding mode of these compounds was proved to be a hybrid binding mode by experiments. The cytotoxicity of synthesized compounds against 4 different human cancer cell lines (EC109, BGC823, SGC7901 and HEPG2) was evaluated by thiazolyl blue tetrazolium bromide (MTT) assay. All of the bis-naphthalimide derivatives exhibited good anticancer activity than the positive control drug (amonafide), which was due to the promotion of reactive oxygen species (ROS) level in test cancer cells by the reversible one-electron redox process of ferrocenyl bis-naphthalimide derivatives. Although there was no obvious relationship between the binding constants and the chain length, the structure cytotoxicity relationship revealed that the linker of n = 3, m = 1 was the best choice for the tested tripodol bis-naphthalimide derivatives. SYNOPSIS: A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized to study the DNA binding ability and the cytotoxicity induced by reactive oxygen species. All of the compounds exhibited good DNA binding ability. And the structure cytotoxicity relationship revealed that the structure of 5h was the best choice.

Organometallic compounds in drug discovery: Past, present and future

In this review, we present an overview of some of the medicinally-relevant organometallic drugs that have been used in the past or that are currently in clinical trials as well as an example of compounds that are currently in the initial stage of drug development. Three main classes of organometallic complexes have been chosen for discussion: antimicrobial organoarsenicals, antimalarial and anticancer ferrocene-containing compounds and anticancer catalytic organometallic complexes. The purpose of this review is to provide readers with a focus on the significant progress that has been made for each of these respective fields of medicine.

Recent advances in iron-complexes as drug candidates for cancer therapy: reactivity, mechanism of action and metabolites

In this perspective, we discuss iron-complexes as drug candidates that are promising alternatives to conventional platinum-based chemotherapies owing to their broad range of reactivities and to the targeting of different biological systems. Breakthroughs in the comprehension of iron complexes' structure-activity relationship contributed to the clarification of their metabolization pathways, sub-cellular localization and influence on iron homeostasis, while enlightening the primary molecular targets of theses likely multi-target metallodrugs. Both the antiproliferative activity and elevated safety index observed among the family of iron complexes showed encouraging results as per their therapeutic potential and selectivity also with the aim of reducing chemotherapy side-effects, and facilitated more pre-clinical investigations. The purpose of this perspective is to summarize the recent advances that contributed in unveiling the intricate relationships between the structural modifications on iron-complexes and their reactivity, cellular trafficking and global mechanisms of action to broaden their use as anticancer drugs and advance to clinical evaluation.

Synthesis and In Vitro Anticancer Activity of 6-Ferrocenylpyrimidin-4(3H)-one Derivatives

AIM AND OBJECTIVE

Some ferrocenyl derivatives are active in vitro and in vivo against cancer. Generally, ferrocenyl derivatives for cancer research have three key components: a ferrocene moiety, a conjugated linker that lowers the oxidation potential and some derivative (peptide, nucleobase and others) that can interact with biomolecules. Since the pyrimidine fragment can easily pass through the membrane into the cells and become involved in metabolism; it appears to be promising. Furthermore, this fragment is an electron-acceptor group, so a spacer can be excluded. Therefore, the synthesis of 6-ferrocenylpyrimidin-4(3H)-one derivatives and the study of their anticancer activity have scientific and practical interest.

METHODS

The syntheses of 6-ferrocenylpyrimidin-4(3H)-one derivatives were performed by the condensation of ethyl 3-ferrocenyl-3-oxopropionate with thiourea or acetamidine or guanidine. The cytotoxicity of four 6- ferrocenylpyrimidin-4(3H)-one derivatives was evaluated by using the MTT assay in vitro against Human breast adenocarcinoma MCF-7 and normal human skin fibroblast HSF cells. The tested derivatives induced a concentration-dependent cytotoxic response in cell lines.

RESULTS

A study of the cytotoxic activity of 6-ferrocenylpyrimidin-4(3H)-one derivatives by the MTT test has found that all compounds have a dose-dependent toxic effect on the lines of breast cancer cells (MCF-7) and normal human fibroblast cells (HSF). The most pronounced cytotoxic effect is exhibited by 2-methyl-6-ferrocenylpyrimidin- 4(3H)-one (MCF-7, IC50 17 ± 1 µM).

CONCLUSION

The experimental results confirm the importance of investigation and design of ferrocenylpyrimidin- 4(3H)-one derivatives as anticancer agents. Compounds where the pyrimidine derivatives are directly linked to the ferrocene unit rather than via a spacer group also may be of interest for antiproliferative drug design.

Novel Polycondensed Partly Saturated β-Carbolines Including Ferrocene Derivatives: Synthesis, DFT-Supported Structural Analysis, Mechanism of Some Diastereoselective Transformations and a Preliminary Study of Their in vitro Antiproliferative Effects

Use of a Pictet-Spengler reaction of tryptamine and l-tryptophan methyl ester and subsequent reduction of the nitro group followed by further cyclocondensation with aryl aldehydes and formyl–substituted carboxylic acids, including ferrocene-based components, furnished a series of diastereomeric 6-aryl-substituted 5,6,8,9,14,14b-hexahydroindolo[2′,3′:3,4]pyrido[1-c]-quinazolines and 5,5b,17,18-tetrahydroindolo[2′,3′:3,4]pyrido[1,2-c]isoindolo[2,1-a]quinazolin-11-(15bH)-ones with the elements of central-, planar and conformational chirality. The relative configuration and the conformations of the novel polycyclic indole derivatives were determined by ¹H- and ¹³C-NMR methods supplemented by comparative DFT analysis of the possible diastereomers. The structure of one of the pentacyclic methyl esters with defined absolute configuration “S” was also confirmed by single crystal X-ray diffraction measurement. Accounting for the characteristic substituent-dependent diastereoselective formation of the products multistep mechanisms were proposed on the basis of the results of DFT modeling. Preliminary in vitro cytotoxic assays of the products revealed moderate-to-significant antiproliferative effects against PANC-1-, COLO-205-, A-2058 and EBC-1 cell lines that proved to be highly dependent on the stereostructure and on the substitution pattern of the pending aryl substituent.

Synthesis, characterization, and anticancer activity of folate γ-ferrocenyl conjugates

Novel folate γ-ferrocene conjugates were synthesized through a regiospecific route, and showed selectivity and enhanced cytotoxicity against Frα-positive malignant cells.

Cyclic Naphthalene Diimide with a Ferrocene Moiety as a Redox-Active Tetraplex-DNA Ligand

Cyclic naphthalene diimides (cNDIs), with a ferrocene moiety (cFNDs) and different linker lengths between the ferrocene and cNDI moieties, were designed and synthesized as redox-active, tetraplex-DNA ligands. Intramolecular stacking was observed between ferrocene and the NDI planes, which could affect the binding properties for G-quadruplexes. Interestingly, the circular dichroism spectrum of one of these compounds clearly shows new Cotton effects around 320-380 and 240 nm, which can be considered a direct evidence of intramolecular stacking of ferrocene and the NDI. Regarding recognition of hybrid G-quadruplexes, the less rigid structures (longer linkers) show higher binding affinity (10⁶  m^-1 order of magnitude). All new compounds show higher selectivity for G4 during electrochemical detection than noncyclic FND derivatives, which further identifies the redox-active potentiality of the cFNDs. Two of the three compounds tested even show preferential inhibition of cell growth in cancer cells over normal cells in a low concentration range, highlighting the potential for bioapplications of these cFNDs.

Importance of Combining Advanced Particle Size Analysis Techniques To Characterize Cell-Penetrating Peptide-Ferrocifen Self-Assemblies

The design of a simple platform to target the delivery of notably hydrophobic drugs into cancer cells is an ultimate goal. Here, three strategies were combined in the same nanovector, in limiting the use of excipients: cell-penetrating peptides, an amphiphilic prodrug, and self-assembly. Light scattering and cryogenic transmission electron microscopy revealed one size population of objects around 100 nm with a narrow size distribution. However, in-depth analysis of the suspension by nanoparticle tracking analysis, small-angle X-ray scattering, and nuclear magnetic resonance (NMR) diffusometry demonstrated the presence of another population of small objects (<2 nm). It has been shown that these small self-assemblies represented >99% of the matter! This presence was clearly and unambiguously demonstrated by NMR diffusometry experiments. The study highlights the importance and the complementary contribution of each characterization method to reflect the reality of the studied nanoassembly.

Oxygen-Functionalized and Ni+x (x=2, 3)-Coordinated Graphitic Carbon Nitride Nanosheets with Long-Life Deep-Trap States and their Direct Solar-Light-Driven Hydrogen Evolution Activity

Graphitic carbon nitride, a 2 D layered photocatalyst coupled with transition metal oxides often shows promising photocatalytic hydrogen evolution activity. However, low surface area and poor charge separation greatly hinder its photocatalytic efficiency. A Ni^+x (x=2, 3)/O-g-C₃ N₄ photocatalyst with a very high specific surface area (199 m²  g^-1 ) has been prepared by thermal condensation and wet-impregnation methods. The oxygen-functionalized and Ni^+x (x=2, 3)-coordinated g-C₃ N₄ produced 1664 μmol g^-1 of hydrogen evolution from water under direct solar light irradiation in 4 h, which is 23 times higher than that over O-g-C₃ N₄ . This significant enhancement results from the combined effects of large surface area, the formation of long-life deep-trap states, effective charge carrier separation, and extended visible light absorption. The separation and transport behavior of the charge carriers are investigated by photoluminescence, time-resolved photoluminescence, photocurrent and Mott-Schottky measurements. Additionally, the interaction between Ni^+x (x=2, 3) and O-g-C₃ N₄ is studied by X-ray photoelectron spectroscopy, X-ray diffraction, and FTIR spectroscopy. The Ni^+x (x=2, 3)/O-g-C₃ N₄ photocatalyst shows remarkable reusability over a period of two months (six cycles). This study may provide a pathway to simultaneously overcome the challenges of low surface area and poor charge separation in g-C₃ N₄ -based photocatalysts.

Platinum(IV)-Ferrocene Conjugates and Their Cyclodextrin Host-Guest Complexes

Reported here are new platinum(IV) (Pt(IV)) complexes bearing ferrocene (Fc) moieties. These systems differ from one another only by the nature of the functional group (ester vs amide) connecting the linker to the Fc subunits. This minor structural variation (one atom difference) leads to major differences in solubility, stability, and antiproliferative activity against lung (A549) cancer cells. The host-guest chemistry of these complexes was investigated in an aqueous medium in the presence of β-cyclodextrins (β-CD), either free or in the form of a covalently linked Fc-Pt-β-CD hybrid. An inclusion complex between Fc and β-CD is formed in aqueous media, presumably as a result of hydrophobic interactions involving the Fc and the inner β-CD cavity. Consequently, it proved possible to use a β-CD-based strategy to purify the Pt-Fc conjugates in this study under aqueous conditions (by means of C18 silica gel columns). The use of a β-CD adjuvant also allowed dimethyl sulfoxide (DMSO) to be avoided as an organic cosolvent in cell studies. The amide version reported here (2) proved to be more soluble, more stable, and more active than the ester analogue (11) in A549 cells. The use of a β-CD functionalized with a fluorescent probe allowed intracellular Pt-Fc localization to be visualized by confocal fluorescence microscopy.

Scope of organometallic compounds based on transition metal-arene systems as anticancer agents: starting from the classical paradigm to targeting multiple strategies

The advent of the clinically approved drug cisplatin started a new era in the design of metallodrugs for cancer chemotherapy. However, to date, there has not been much success in this field due to the persistence of some side effects and multi-drug resistance of cancer cells. In recent years, there has been increasing interest in the design of metal chemotherapeutics using organometallic complexes due to their good stability and unique properties in comparison to normal coordination complexes. Their intermediate properties between that of traditional inorganic and organic materials provide researchers with a new platform for the development of more promising cancer therapeutics. Classical metal-based drugs exert their therapeutic potential by targeting only DNA, but in the case of organometallic complexes, their molecular target is quite distinct to avoid drug resistance by cancer cells. Some organometallic drugs act by targeting a protein or inhibition of enzymes such as thioredoxin reductase (TrRx), while some target mitochondria and endoplasmic reticulum. In this review, we mainly discuss organometallic complexes of Ru, Ti, Au, Fe and Os and their mechanisms of action and how new approaches improve their therapeutic potential towards various cancer phenotypes. Herein, we discuss the role of structure-reactivity relationships in enhancing the anticancer potential of drugs for the benefit of humans both in vitro and in vivo. Besides, we also include in vivo tumor models that mimic human physiology to accelerate the development of more efficient clinical organometallic chemotherapeutics.

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD⁺/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., ¹O₂ production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.